Hi Suneel,
SendKeys in any programming language is not a fully reliable option for automating anything. For SendKeys to work at least a bit you need to activate the right window and correctly place the focus on the desired textbox which is the trickiest part.
However, for properly writing anything to a web page element (say textbox) you need to spy that textbox using the Application Modeller, then use the Writer stage to input anything to that textbox.